This invention relates to an optical semiconductor diode driver circuit and optical transceiver modules. In more detail, the invention relates to an optical transmission device used for optical communications or optical data links, and more particularly, to an optical semiconductor diode driver circuit and optical transceiver modules fully operative with a low voltage power supply, under a severe condition that the difference between a forward bias voltage of the diode and a power supply voltage for the driver circuit, required for driving the optical semiconductor diode, is fairly small.
The currently rapid growth multimedia is supported by various network backbones from WAN (wide area network) to LAN (local area network). Among them, optical communication and FDDI (fiber distributed data interface) are typically used, for which high-speed and high-performance optical transmission devices are indispensable. Recently, in particular, not only for high-speed telecommunication but also for the application to data communication between computers, the need for reliable and high-throughput optical interconnection technologies is progressively increasing.
To cope with the requirement, fiber channels and IEEE 1394 have been standardized and several data links with use of optical fibers are going to be developed. As downsizing of computers is also progressing rapidly, PC (personal computers) and/or EWS (engineering workstation) become a standard data processing tool. So, regarding specifications required for interconnection, much importance has been attached to applicability from a practical viewpoint in addition to a high performance in throughput. That is, from the viewpoint of practical application to a system, there is a demand for devices operative with a low power consumption for abbreviation of a cooling system, with the same electrical input/output interface as that of ICs used in a computer system, and preferably with the same power supply voltage. From the viewpoint of the cost effectiveness of the system, there is a strong demand for realization of low-cost optical transceiver modules.
Especially in the IEEE 1394 standard just fixed, for purposes of reducing the link cost by optical fibers and optical transceiver modules, it is presumed that the combination of plastic fibers and a light source of the red wavelength band matched to a low transmission loss through fibers will be rapidly grown. A semiconductor laser diode (LD) oscillating with a wavelength of about 650 nm is used as a light source of the red wavelength band.
However, through investigations by the Inventor, employment of such a red LD has revealed to cause a new problem different from those of optical transmitters in conventional optical telecommunication using infrared LDs with wavelength bands longer than 1.3 um. This problem is as follows.
In case of an optical communication device using the infrared LD, since the photon energy emitted from the LD is 1 eV or less, the applying voltage to the LD under operation is from 1.2 V to 1.5 V at most. However, since the photon energy is inversely proportional to the wavelength and the band gap energy of the semiconductor is proportional to the photon energy, the forward bias voltage of the diode required for operation of the optical semiconductor diode with a red region becomes high compared with the infrared LD. For example, in case of LD oscillating at a wavelength of 650 nm or less, the forward voltage necessary for the LD drive is at least 2 V. Considering it into account of the voltage drop due to an internal resistance increase and/or the need for a large driving current, it must be expected that the forward voltage increases to about 2.5 V maximum.
On the other hand, a usual power supply voltage for operating recent signal processor ICs or memory ICs is being reduced from 5 V to 3.3 V, and also the voltage of 3.3 V or less is expected to be the standard in a near future. Additionally, the finer micro-processes for decreasing the power consumption of signal processor ICs and for getting their processing speed have been developed one after another, and the shift of decreasing the internal operation voltage inside ICs to the order of 2 V or less is also rapid. However, in order to avoid complexities and cost-increasing disadvantages on building the system with mixing interfaces of different voltage levels, it is a general trend that input/output interfaces of ICs are brought into matching with the common logic level of the 3.3 V system, even when the IC internal operation voltage is lower than 3.3 V.
Therefore, it is important to realize a LD driver circuit that can be designed to guarantee a fully functional operation on a single 3.3 V power supply. In other words, it is indispensable to realize a diver IC capable of driving the LD with the forward bias voltage of 2.5 V, maximum, on a power source of 3.3 V. Even if we consider just 5% fluctuation in power supply voltage that is the minimum requirement for any system, the difference between the source voltage and the forward operation voltage of LD is 0.635 V only. If we suppose that a maximum power supply change of 10% is allowed as in popular cases and a voltage drop by wiring resistance inside an IC package is assumed to be small of 47 mV, the voltage difference may decrease by 0.4 V.
FIG. 27 shows a schematic circuit diagram of a conventional LD driver circuit. Since the conventional driver circuits have been usually designed to operate with a source voltage of 5 V or a higher voltage, a sufficient output voltage for a LD operation was ensured, which is much greater than the forward voltage of LD. Then it was easy to share a voltage necessary for a current switching transistor and a control transistor of a constant current source in the LD driver circuit respectively. Therefore, as shown in FIG. 27, the stacked configuration of the two sub-circuits, a differential transistor switch circuit and a high-accuracy constant current generating circuit, has been widely employed to ensure high-speed and relatively large switched current, and precise output amplitude in the driver IC.
Here the LD driver circuit shown in FIG. 27 is illustrated briefly but more concretely. This circuit includes a pre-driver circuit at its input portion and a large-current switch output circuit at its output stage. The pre-driver works as a pulse shaper, which is made up of a differential limiting amplifier and emitter followers. The output circuit is made up of differential transistors for switching on and off the current of the constant current source according to the high and low level of the logic input respectively. And also a constant current source is connected to the collector of the final output transistor for applying a DC bias current to the LD. In order to achieve a properly functional operation of the output stage on this circuit configuration, it is important to keep the total voltage margins of the collector-emitter bias sufficient for non-saturated operation of the output differential switching transistors, and necessary for operating the constant current source connected to their emitters.
FIG. 28 shows voltage-current characteristics of a typical high speed npn transistor. When the base-fixed constant current generating circuit in FIG. 27 is designed on trial considering such npn transistor characteristics as shown in FIG. 28, it has been confirmed that the total voltage necessary for the reference resistance bias and the collector-emitter voltage of the control transistor for the constant current source is more than 0.5 V, even if paying careful attention to minimizing the operation biases. However, to design a 3.3V driver IC with use of the above configuration, even when assuming the aforementioned voltage difference 0.635 V, if it is pile up thereon, the voltage that can be applied to the switch transistor is about 0.1 V only. Then it is impossible to achieve the normal operation of the switch transistors in the linear region.
This problem might be solved by supplement an insufficient voltage assisted by a DC-DC converter circuit inside IC for generating a higher voltage or a negative voltage from positive source input. In this case, however, since the current for driving an optical semiconductor diode is usually as relatively large as at least decades of mA, a larger current supply capacity is required in the increased or negative internal voltage generating circuit, which results in the need for an additional external capacity or the need for a massive inductor, and therefore makes it difficult to realize a LD drive circuit as a one-chip IC. Furthermore, there occurs another problem that power consumption of an IC as a whole increases because of a loss in the voltage converter circuit for generating the different voltage in addition to an essential increase in power consumption caused by the increase in effective source voltage to get a normal operation of the circuit.
As discussed above, if a red optical semiconductor diode with the high forward operation voltage will try to be driven by IC on the 3.3 V power supply, the driver circuit of the conventional configuration inevitably reveals a bias voltage shortage of internal transistors on IC, so that it is difficult to output the desired pulse waveform.
Additionally, the conventional countermeasure for overcoming the above problem involved great problems from the practical viewpoint, because it caused various drawbacks such as increase of the power consumption and impossibility of realizing one-chip ICs due to the need for adding external capacitors and/or inductor.
Based on recognition of these problems, it is an object of the invention to provide an optical semiconductor diode driver circuit reliably operating even with the supply of a source voltage slightly higher than a forward operation voltage of an optical semiconductor diode to be driven, capable to output a switched current and voltage large enough to drive the optical semiconductor diode, and realizing the ability of an arbitrary and variable setting of its output current with a high accuracy and compactness facilitating its design as a one-chip IC, and to provide optical connector coupled plastic optical transceiver modules. According to the invention, there is provided an optical semiconductor diode driver circuit comprising:
a pre-driver circuit including functions of amplification but limiting the maximum amplitude of the output voltage of the amplifier to a predetermined value, operating as a limiter-type amplifier, so as to amplify and shape an input pulse wave form and generate differential voltage pulses; and
an output circuit responsive to the differential voltage pulse output from the pre-driver circuit to output externally a drive pulse current to an optical semiconductor diode as a load, the output circuit including a first transistor and a second transistor whose emitters are commonly connected at a common node; and both of a variable constant current source and a resistor connected to the common node, the differential voltage pulse outputs from the pre-driver circuit being input to the base of the first and the second transistors, the second transistor outputting a collector output current as the drive pulse current,
when the voltage pulse input to the base of the first transistor exhibits a low level, the first transistor taking a cut-off state and the second transistor taking a constant-current on-state close to a saturated operation; when the input level of the voltage pulse rises to a high level, the first transistor taking a constant-current on-state close to a saturated operation and the second transistor taking a cut-off state; and in a transient state between the cut-off state and the constant-current on-state, emitter current feedback by the resistor being activated to switch sharply and mutually invert the state of the first transistor and the second transistor.
The above-summarized construction promises realization of a compact optical semiconductor diode driver circuit which operates with the power supply of a source voltage slightly higher than a forward operation voltage required for driving the optical semiconductor diode, can variably set the current output to the optical semiconductor diode at a desired value with a high accuracy, and is readily made as a single-chip IC.
The pre-driver circuit may further include a level shifter for adjusting the average output voltage level of the amplifier, and supplied with another power source different from the output circuit, the voltage of which being always maintained constant independently of operative condition changes of the circuit, the level shifter having a level shift resistor and a temperature-dependent constant current generating circuit to compensate temperature change of the switching voltage level of the amplifier.
This construction ensures a property of the output current pulse waveform to the optical semiconductor diode in which the pulse width and the transient response are maintained constant, and temperature dependency of the output current amplitude compensates optical output deterioration of LD against the change of operating temperature.
The variable constant current source of the output circuit may generate a specified current having a negative temperature dependency, the amplitude of the current pulse output from the second transistor being compensated to maintain a constant value even upon a change in temperature.
This construction ensures that the pulse current amplitude be maintained constant independently of the operative temperatures of IC.
Alternatively, the variable constant current source of the output circuit may generate a compensation current component having a negative temperature dependency in addition to a bias current component of a constant value, the amplitude of the current pulse output from the second transistor being controlled by the bias current component to maintain a constant value, and the amplitude of said current pulse being compensated by the compensation current component to maintain a constant value even upon a change in temperature. This construction ensures the capability of setting desired accuracy and value while maintaining the pulse current amplitude constant independently of operative conditions of IC.
Alternatively, the variable constant current source of the output circuit may include:
an emitter-grounded transistor of a size n which is connected in parallel between the common node and the ground connection;
a unit transistor of a size 1 including a collector connected to the common node and a base connected to the base of the transistor of the size n, in which a constant current in the amount of 1/(n+1) of a current value biased to said common node flows; and
an error amplifying/feedback circuit network for supplying a feedback signal to the base of the transistor of the size n and the base of the transistor of the size 1 to always maintain zero as the voltage difference between the emitter of the unit transistor and the ground connection.
This construction ensures realization of high-accuracy current adjustment function increasing the reference current accuracy and decreasing influences from changes in current amplification ratio or fluctuation in source voltage caused by fluctuation of the load when a small-current negative power source is usable.
Alternatively, the output circuit may further include a constant current generator connected to the collector of the second transistor to add a DC bias current of a constant value to the drive pulse current.
This construction makes it possible to add a temperature-dependent current generating circuit for precisely controlled LD DC bias in form of a compact circuit arrangement to thereby ensure good high-frequency operation of LD.
Additionally, another optical semiconductor diode driver circuit according to the invention has a construction similar to a Schmitt circuit as one of its features, as listed below.
That is, according to the invention, there is further provided an optical semiconductor diode driver circuit comprising: a pre-driver circuit including both functions of amplification and limiting the amplitude of the output voltage of the amplifier to a predetermined value, operating as a limiting amplifier, so as to amplify and shape an input signal and generate a voltage pulse; and
an output circuit responsive to the voltage pulse output from the pre-driver circuit to output externally a drive pulse current to an optical semiconductor diode as a load, the output circuit including a first transistor and a second transistor whose emitters are commonly connected at a common node; and both of a variable constant current source and a resistor connected to the common node, the differential voltage pulse output from the pre-driver circuit being input to the base of the first transistor, the second transistor outputting a collector output current as the drive pulse current.
The current output circuit can be operated by any of two kinds of systems. One of them is a system to have the collector-emitter voltage of the switch transistor to execute switching operation in the saturation mode region. The other is a system to have the collector-emitter voltage execute switching operation within the non-saturated mode region.
In the non-saturated system, the circuit is implemented with a proper bias setting of the high level of the base input pulses by the pre-driver circuit and a voltage dividing resistor network carefully optimized in its value. In this manner, the circuit executes a non-saturated operation in the current-switch-on state to make the output pulse amplitude a certain constant. With the non-saturated current switching operation, it is possible to realize the operation including the function of regulating the current pulse amplitude dependent on the setting.
Typically, an independent circuit using a base-grounded transistor amplifier to output from the collector a constant current regulated by the base bias voltage and the emitter load resistor is for the basic constant current generating circuit. In contrast, the invention attains the operation mode for outputting a constant current in a period of the pulse high state and for reducing the output current to zero in a period of the pulse low state by driving the base with a rectangular pulse instead of normally fixing the base voltage bias.
Alternatively, the optical semiconductor diode driver circuit according to the invention comprises: a pre-driver circuit including both functions of amplification and limiting the amplitude of the output voltage of the amplifier to a predetermined value, operating as a limiting amplifier, so as to amplify and shape an input signal and generate a voltage pulse; and
an output circuit responsive to the voltage pulse output from the pre-driver circuit to output externally a drive pulse current to an optical semiconductor diode as a load, the output circuit including a first transistor and a second transistor whose emitters are commonly connected at a common node; and both of a variable constant current source and a resistor connected to the common node, the differential voltage pulse output from the pre-driver circuit being input to the base of the first transistor, the second transistor outputting a collector output current as the drive pulse current, when the voltage pulse input to the base of the first transistor exhibits a low instantaneous level, the first transistor taking a cut-off state and the second transistor taking a saturated state or a constant current on-state, when the input level of the voltage pulse rises above a predetermined value, the first transistor taking a saturated state and the second transistor taking a cut-off state, in a transient state between the cut-off state and the saturated state or the constant current on-state, positive feedback being activated to rapidly switch and invert the first transistor and the second transistor.
That is, the input signal is first input to the pre-driver circuit, and then amplified and shaped into a rectangular pulse signal having an amplitude optimum for driving the output circuit stage. The pre-driver circuit is basically a differential limiting amplifier, in which the amplitude has a substantially constant value and an output pulse with smaller rise and fall time constant is obtained. Moreover, the high level voltage of the output pulse regulates the peak value of the amplitude of the output pulse current from the final stage output circuit.
The limiting amplifier circuit contains a level shift resistor therein, and the DC level of the output pulse voltage is designed to have a property of maintaining its high level at a constant value or decreasing the high level with temperature by adding a slight amount of positive temperature coefficient to the voltage generated in the level shift resistor, thereby to decrease temperature change of the input discrimination level of the output stage switch circuit transistor. The shaped and amplified voltage pulse signal is input to the output circuit in form of an emitter-coupled pulse amplifier whose basic circuit arrangement is similar to a Schmitt circuit, and it is converted to supply an ON/OFF modulated pulse current to LD connected to the output-side transistor as an external load.
In case of the saturated-type switch circuit, the collector-emitter voltage of the output circuit transistor is operated in the completely saturated mode region.
However, in case of the non-saturated switching system, the first and second transistors in the current switch output circuit changed between two states, namely, the off-state blocking the current and the on-state in which the collector-emitter voltage does not drop to the saturation voltage, and a constant current flows while maintaining a constant voltage enabling normal operation of the transistor.
More specifically, in the output circuit, a pre-driver output pulse signal voltage is input to the base of the first transistor, and a resistor is connected to its collector as a load. At the connection point of the collector and the load resistor, one terminal of the second resistor is connected and the other terminal of the second resistor and the third resistor are connected in series and then to the ground, and the base of the second transistor is connected to the node of the second and third resistors. In order to improve the transient response of the output waveform by efficiently transferring a high-frequency components to the base, a capacitance is provided in parallel with the second resistor.
Emitters of the first and second transistors are commonly connected, and then to the ground potential via a fourth resistor. Therefore, it is a kind of pulse amplifier to which current feedback is applied by the impedance of the fourth resistor. At the common node of the emitters, a constant current source is connected additionally, and by appropriately adjusting the current value generated therefrom, control is made to ensure a current of a desired value to flow to LD connected as an external load, using the collector terminal of the second transistor as the output.
In case of the saturated-type switching circuit system, values of the second and third resistors are determined basically to feed the sufficient base bias current to cause a saturated operation of the second transistor. If there is no constant current source connected to the common emitter, the current value flowing in LD is determined by the external supply source voltage, diode forward matching voltage and internal operation resistance as electric properties of LD, and the value of the fourth resistor.
In the non-saturated type switching operation circuit, the output current applied to LD is determined by a current summing a current made by dividing the emitter voltage of the second transistor, whose base voltage is fixed by divisional voltages of the second and third resistors, by the fourth resistor value and an output current value of the constant current source connected in parallel to the fourth resistor.
Especially when the output load current is changed, the output current pulse width also is modified due to a change in mean base injection current of the second transistor. However, by optimizing the base bias voltage of the second transistor, modification of the output pulse width can be minimized. To realize it, a method of injecting to the node of the second and third resistors a current bias of a fractional value proportional to the constant current source connected to the common emitter.
In case of the saturated-type switch output circuit, it is just a Schmitt circuit when the collector load of the second transistor in the output circuit is a pure resistor. However, since it is LD different from a pure resistor, the impedance largely varies with operational conditions, the current injected to LD largely varies with change of power source voltage and/or operating temperature.
The constant current source connected to the common emitters is implemented with the role of realizing a property of always maintaining a desired output current value preset in LD by adjusting the pulse amplitude of the on/off current and simultaneously adjusting the output current value appropriately according to changes of the operational environment such as power supply voltage or temperature variation. As a result, behaviors of the output circuit are substantially equivalent to those of a Schmitt circuit, and the high/low discriminating level for the input voltage exhibits a certain hysteresis, and a rectangular pulse with a small transient response time is obtained at the output end. Needless to say, these specific numerical values of the characteristics may depend on the actual design of the circuit. While the constant current source basically has an output impedance of a very large value, the value of the fourth resistor connected to the common emitter is a small value. Therefore, the impedance between the common emitters and the ground is not affected by the output value of the constant current source.
Although the contents set forth in the foregoing paragraphs are not directly applicable to the non-saturated type switch circuit, the non-saturated switch circuit can also work similarly. In that quick logic inversion sequences upon transient response operation of the switch, a current positive feedback is happened effectively, so that the circuit exhibits a hysteresis between the input on and off transition levels and behaves similarly to a Schmitt circuit, and also that the high-frequency operation property is not affected by load variation of the constant current source regarding the emitter current feedback property. Additionally, when a capacitance is added in parallel with the emitter resistor as explained below, it operates as peaking to the transient response. The peaking capacitance value optimum therefor may be determined as the value obtained by subtracting the parasitic capacitance and the collector effective capacitance in the constant current circuit from the ideal optimum capacitance value connected intentionally.
Basically, in the output stage circuit, operation of the output transistor is not stayed within the linear active region but limited by the on/off saturated regions in the saturated switch output circuit system. On the other hand, in case of the non-saturated switch system, on/off modulated pulse current alone is also permitted to flow in LD as the external load because the output transistor takes either a cut off state or the current-on-state where the collector-emitter voltage keeps finite nearly in the saturated region. On the other hand, in order to ensure a high-frequency property of LD, it is necessary to always apply a DC bias current up to the proximity of the threshold of LD.
To meet this requirement, there is a usual method for supplying a DC current bias from the exterior. However, since it must be supplied with high impedance at high-frequency ranges without pulse distortion, it is indispensable to use an expensive and large part like a bias T, so that a low-cost and compact optical transmitter cannot be realized. To overcome this problem, it is effective to use the method of implementing a constant current source inside IC and directly connecting it to the collector terminal of the output transistor.
Additionally, by combining a capacitance in parallel with the fourth resistor and implementing a time constant of 1 ns or less so as to apply high-frequency peaking to the amplification gain of the output circuit, reduction of the transient response time of the rectangular pulse output waveform and increase of the maximum operation frequency can be realized.
In the case where the pre-driver circuit of the emitter follower output is simply connected to the final stage output circuit, there is produced a property in which the base-emitter voltage drops with increase of the temperature, the discrimination level shifts, the current pulse width loaded to LD changes, and the pulse duty ratio of the transmission waveform changes.
In order to prevent substantial change of the discrimination level, the level shift resistor of the pre-driver circuit may be configured to generate an opposite voltage change large enough to just compensate the temperature variance of a number of equivalent diodes corresponding to a half of the total number of transistors used in the emitter follower of the pre-driver circuit. In order to implement the voltage drop a positive temperature coefficient, a constant current source having a positive temperature coefficient may be additionally connected to the common node of two collector load resistors of a differential limiting amplifier and the level shift resistor such that the product of the current changing rate and the level shift resistor value coincides with the value obtained by multiplying approximately 1.2 mV/xc2x0C. per unit diode by the number of the equivalent diodes.
Although the non-saturated switch output circuit system basically operates in the same manner, it is necessary not only to prevent change of the pulse width duty ratio but also to prevent variation of the current amplitude of the output. In order to control the LD output current itself desirably, there are the emitter current, resistance ratio of voltage divisional network, temperature-dependent bias value applied thereto, and so forth, as parameters to be adjusted. Some different kinds of circuit systems may be designed, according to which combination of the parameters should be selected.
Although the frequency bandwidth of a pnp transistor is usually a problem depending on usable processes, it is much smaller than that of an npn transistor at least by one digit. In the case where. a pnp transistor cannot be used as the constant current source directly connected to the common emitters of the output circuit due to the high frequency characteristics, the use of the constant current circuit becomes difficult. To overcome this problem, it is effective to connect the collector and the emitter of an npn transistor between the common emitter and the ground connection and introduce a feedback voltage of an error amplifier into the base to control it. That is, the transistor making up the current source must have a size corresponding to an expected maximum amount of current generation, and one with the size as large as n times the basic transistor is used. Simultaneously, another transistor of the basic size is commonly connected to the collector and the base, and the emitter is connected to a negative reference power source via a reference resistor.
By appropriately selecting values of the reference voltage and the reference resistor, a current 1/(n+1) of the current value desirable to set as the current source is ensured to flow. When it is desirable that the determined current Icd has a certain property, the reference voltage is designed to have a property of changing by the same rate.
In this circuit configuration, control is made by amplifying the error voltage so as to always maintain zero of the voltage difference between the node of the emitter and the reference resistor and the ground potential, and feeding it back to the base voltage.
If the maximum collector current is selected such that collector-emitter voltage making the voltage vs. current characteristics of the basic transistor to avoid the saturation property be larger than the terminal-to-terminal voltage of the fourth resistor, then it is possible to increase the operation impedance to a value as large as tens times the value of the fourth resistor even when (n+1) basic transistors operate in parallel, and substantially the same electrical property as that obtained by connecting the constant current source can be maintained.
Although it is different from the above-explained constant current generating circuit system using the negative power source in a strict sense, it is possible to use a constant current circuit employing a current mirror circuit as a circuit system quite similar to the said circuit from the viewpoint of the basis of operation of the constant current circuit and not using the negative power source. However, attention is paid to the difference between these two systems.
The former, not using pnp transistors typically with a low cut-off frequency, has merit with a wider band and also demerit of its need of a negative voltage reference source. In contrast, however, it has the features that the use of the negative voltage enables a higher accuracy of the reference current, changes in the output current caused by fluctuation of the load are small as excellent characteristics of a typical npn transistor, and influences from variation of the source voltage are also small.
On the other hand, as to the latter, it is important features that it can operate with a single power source only and can be made easily as a one-chip IC.
When the LD driver circuit is used, it is possible to realize a transceiver module coping with a low power voltage source, which is operable even with a small difference between the forward applied voltage of LD and the source voltage.
The transmitter module contains a sub-module collectively packaging on a substrate an IC incorporating the LD driver circuit, LD, capacitors, resistors, and so forth, as additional parts for complete operation of the module, and it is molded in a plastic package by collective molding, having including leads for electrically coupling and an optical connector for optically coupling to the optical fiber cables.
As a result, a compact transmitter module has been realized, which operates with a single power source commonly used to supply a source voltage to other signal processing ICs, and decreases the consumption power low enough to permit use of a small heat sink or no use. By simultaneously packaging an optical receiver on the sub-module, an optical transceiver having the same features can be realized.
The invention enables realization of a compact optical semiconductor drive circuit easy to make as a one-chip IC, which stably operates only with the supply of a source voltage slightly higher than a forward operation voltage of an optical semiconductor diode to be driven, and can variably determine the current output to the optical semiconductor diode at desired accuracy and value.
As a result, the invention can inexpensively provides a compact optical connector coupled plastic optical transmitter and transceiver modules which operates with a single power source commonly used to supply a source voltage to other signal processing ICs, and decreases the consumption power low enough to permit the use of a normal design for heat radiation.